The mitral valve lies in the left side of the heart and the tricuspid valve in the right. These valves, especially the mitral valve, if significantly damaged require repair or replacement. The normal mitral and tricuspid valves have different anatomy the annulus of mitral valve is somewhat "D" shaped, while the annulus of the tricuspid valve is more nearly circular. Valve dysfunction can lead to stenosis a restriction to flow or regurgitation, or both.
A surgically repairable valve often has a dilated annulus. This dilatation may prevent full coaptation of valve leaflets, while an asymmetrical annular dilatation may result in incomplete leaflet coaptation and hence leakage of the valve. Consequently, most repair procedures involve remodeling and stabilization of the annulus by implanting an annuloplasty ring to reduce in the overall size of the valve annulus. When repairing the mitral repairs it is necessary to preserve the normal distance between the two fibrous trigones located adjacent to the anterior leaflet. In this region a definitive annulus is absent. Alteration of the inter-trigonal distance could lead to distortion of the aortic valve with possible aortic regurgitation or left ventricular outflow obstruction. Thus an effective annuloplasty ring should ensure that the natural inter-trigonal distance is neither increased nor diminished by the valve repair procedure.
The prior art regarded as most pertinent to the present invention is incorporated herein by reference to provide a comprehensive background setting to enable better understanding of the present invention and its advantages. The incorporated prior art is tabulated hereinafter, and the features of the prior art considered most closely related to the problems faced in the prior art that are overcome by the present invention are discussed in some detail hereinafter.
Various prostheses have been described for use in conjunction with mitral or tricuspid valve repair. Each has disadvantages. The ring developed by Dr. Alain Carpentier U.S. Pat. No. 3,656,185 is rigid and flat. Although widely used, criticism of its inflexibility preventing the normal alteration in size and shape of the mitral annulus with the cardiac cycle has been widespread. The complication of left ventricular outflow tract obstruction has been described in association with this device. This complication can take the form of a decrease in the dimensions of the left ventricular outflow tract, or systolic anterior motion of the anterior leaflet of the valve. Both complications were reported by Geller M, Kronzon I, Slater J et al. "Long-term follow-up after mitral valve reconstruction: incidence of postoperative left ventricular outflow obstruction". Circulation 1986;74 supp. I I-99-103. They implanted Carpentier rings in sixty-five patients. All sixty surviving patients were restudied 1-55 months postoperatively. All showed a significant decrease in the dimensions of the left ventricular outflow tract, and 6 patients 10% also had systolic anterior motion SAM. Another complication of the Carpentier ring has been inflow obstruction. This complication associated with its use in tricuspid valves was reported by Carpentier et al. in nine of seventeen patients Carpentier A, Deloche A, Hanania G, et al. "Surgical management of acquired tricuspid valve disease". J Thorac Cardiovasc Surg 1974;67:53-65. In addition, the Carpentier ring has the disadvantage of not being of adjustable size. Thus the surgeon has to accurately judge the correct size of ring needed to reduce the annulus size and produce a competent valve.
An open ring valve prosthesis was described in U.S. Pat. No. 4,164,046 comprising a uniquely shaped open ring valve prosthesis having a special velour exterior for effecting mitral and tricuspid annuloplasty. This ring was not adjustable in size during or following implantation. The fully flexible annuloplasty ring described by Carlos D. Duran and Jose Luis M. Ubago, "Clinical and Hemodynamic Performance of a Totally Flexible Prosthetic Ring for Atrioventricular Valve Reconstruction" Annals of Thoracic Surgery, No.5, 458-463, November 1976 could only be shortened in the posterior segment by the placement of plicating sutures. The judgement of the position, size and spacing of these sutures requires skill and experience. However, inappropriate suture placement in the anterior segment could cause undesirable intra-trigonal shortening. Adjustable annuloplasty rings were described by Dr. William Angell U.S. Pat. No. 4,042,979 and Dr. Miguel Puig-Massana U.S. Pat. No. 4,290,151. Both incorporate draw-strings capable of reducing the size of the posterior portion of the ring. The former contains a rigid or flexible member in the anterior leaflet portion of the ring. The latter ring is also adjustable but fully flexible. With this device the use of a continuous implantation suture was recommended rather than the more generally used interrupted sutures. With the Puig-Massana ring the use of interrupted sutures would be likely to interfere with the internal drawstrings. However, should a continuous suture be used for implantation, and the ring then contracted by the internal drawstrings, loosening of the continuous suture would be caused by the reduction in the circumference of the annulus. A further disadvantage of Puig-Massana's ring is that following the tightening of the drawstrings, a bulky knot is formed on the atrial surface of the ring. Hence, the knot lies in the direct blood flow path into the inflow of the valve. Should a thrombus form on the knot it could later embolize. In addition, should the surplus drawstrings be cut too close to the knot, there is the danger of the knot becoming undone. Conversely, should significant surplus drawstrings tails remain, abrasion of the valve leaflets could occur. The adjustable ring by Dr. Ali Ahmadi has the disadvantage of being circular, which is not an appropriate shape, particularly for the mitral annulus.
The rigid rings described above were probably conceived on the assumption that the mitral annulus is "D" shaped and lies in a single flat plane. That this was a misconception was shown by Levine, R. A., Triulzi, M. O., Harrigan P., and Weyman,A. E. "The relationship of mitral annular shape to the diagnosis of mitral valve prolapse", Circulation 75, No. 4, 756-767, 1987. This work shows that the mitral valve annulus is a complex and mobile structure and demonstrated that the mitral valve takes the form of a central, elliptical portion of a hyperbolic paraboloid or saddle shaped surface. It is clear that imposing a flat ring or even a segment of a flat ring would distort the annulus and could cause left ventricular outflow tract obstruction.
Wright and Elliott, U.S. Pat. No. 5,674,279, describe annuloplasty and suture rings in the form of adjustable, flexible tricuspid and tricuspid annuloplasty rings having internal drawstrings that merge from the rings on the annular faces so that the drawstring knots are out of the bloodstream. The drawstrings are contained in clearly marked channels. The mitral ring has a curved semi-flexible stiffener member in the anterior segment to maintain intertrigonal distance during implantation. While the Wright and Elliott device solved many of the problems inherent in the prior art devices, there remains a need for flexible tricuspid and tricuspid annuloplasty rings that assure that the orifice defined by the ring remains substantially constant in cross-section without undue interference with the movement of the surrounding tissue.
The present invention is embodied in annuloplasty ring structure that in large measure overcome the disadvantages of the prior art and provides improved performance and reliability.
It is an objective of this invention to provide a fully flexible, annuloplasty rings specific for use in mitral and tricuspid valve repair.
It is a further objective of this invention to provide a mitral annuloplasty ring in which the inter-trigonal distance and anterior segment is maintained during implantation.
It is a further objective of this invention to provide an annuloplasty ring which is flexible yet which resists plication (puckering) by the action of the implantation sutures.
It is a further objective of this invention to provide a mitral annuloplasty ring that is flexible in an undulating manner so as to follow the change in shape of the mitral annulus, in the plane of the annulus.
It is a further objective of this invention to provide a mitral annuloplasty ring that is flexible about the posterior portion of its circumference, and that prevents restriction of the left ventricular outflow tract.
It is a further objective of this invention to provide a mitral annuloplasty ring that is flexible about the anterior portion of its circumference, and that prevents restriction of the left ventricular outflow tract.
It is a further objective of this invention to provide an annuloplasty ring that is technically easy to use.
Other objectives and advantages of this invention will be more apparent from the detailed description of the device which follows.